This invention relates to permanent magnet couplings. More specifically, this invention relates to a high strength permanent magnet coupling including samarium-cobalt magnets and mounting methods therefor.
Permanent magnet couplings are well known in the prior art, and typically comprise a pair of axially or radially opposed magnets or sets of magnets formed from a permanent magnet material, such as alnico. One of the permanent magnets is coupled to a driving member such as a motor, and the other permanent magnet is coupled to a driven member such as a pump impeller. The magnets are magnetically coupled to each other such that rotation of the driving member causes a corresponding rotation of the driven member to obtain the desired torque output. Couplings of this type are particularly advantageous wherein a hermetic seal or barrier is interposed between the driving and driven members, such as in a motor-driven freon compressor. In these applications, the hermetic seal assures against passage or leakage of any process fluid between the driving and driven members, and thereby prolongs the operating life of the equipment. For examples of prior art magnetic couplings, including hermetic seals or barriers, see U.S. Pat. Nos. 3,877,844; 3,826,938; 3,411,450; 3,512,903; 3,378,710; 3,249,777; 3,238,883; 3,238,878; 3,195,467; 2,970,548; 2,366,562; 2,230,717; and Re. 26,094.
During operation, a magnetic coupling may generate substantial quantities of heat due to relative slippage of the magnets at excessive torque loads, induction heating effects, and the like. This is particularly true with closely aligned, radially interfitting permanent magnets rotating at relatively high speeds such as on the order of about 100,000 rpm. Accordingly, prior art magnetic couplings typically have not been used with mechanical devices rotating at relatively high speeds so as to avoid any cooling requirement. However, some attempts have been made to cool a magnetic coupling, and have typically comprised methods of exposing at least a portion of one of the magnets to a cooling fluid. See, for example, U.S. Pat. Nos. 3,238,883; 3,238,878; and 3,267,868. These prior art devices have not, however, provided the requisite pumping or cooling action required with high speed rotating machinery such as turbomachines.
Another problem in the design of magnetic couplings is the prevention of demagnetization due to copling slippage at high speeds and/or high torque conditions. That is, with magnetic couplings, the maximum coupling torque available is limited to the magnetic and structural characteristics of the magnets. Typically, prior art permanent magnets constructed for structural integrity at high speeds have not provided a magnetic field of sufficient strength for slippage-free coupling under high torque conditions. Some permanent magnet materials capable of providing such high torque coupling, such as rare earth-cobalt magnets, have not been satisfactorily used because of structural brittleness. Specifically, a magnetic coupling has not been provided including high magnetic strength, structurally brittle magnets wherein cracking or breaking of the magnets due to centrifugal force effects at high speeds is prevented.
Prior art magnetic couplings have also encountered bearing design problems. That is, with low speed rotating devices, magnet-carrying shafts may be satisfactorily supported by relatively simple journal and thrust bearing structures such as sleeve bearings, ball bearings, and the like. However, as rotational speed increases, the problems of shaft stability and vibration correspondingly increase to create bearing design and cooling problems. Moreover, with increased speed, the adverse effects on the system due to incidental bearing magnetization and induction heating become substantial. Nevertheless, the prior art has consistently relied upon relatively conventional bearing structures for shaft support. See, for example, U.S. Pat. Nos. 3,512,903; 3,378,710; 3,195,467; 3,238,878; 2,970,548; and 2,366,562. Accordingly, permanent magnet couplings in the prior art have not been widely or satisfactorily used in high speed applications.
This invention overcomes the problems and disadvantages of the prior art by providing an improved permanent magnet coupling particularly for use with relatively high speed rotating machinery. In particular, the invention includes relatively brittle, high magnetic strength samarium-cobalt permanent magnets mounted for structural integrity under high speed rotating conditions.